At the end of the premiere of the Kronos Quartet's new piece, Sun Rings, at Iowa University, there was a large cheer as Dr Donald Gurnett, an eminent local boffin, made his bow. It was an acknowledgement of a lifetime designing instruments for collecting extraordinary sounds from the cosmos.

His work ranges from the days of the early satellites to what he calls the "grand tour" of the Voyager space mission, which has sent back information from Saturn, Jupiter, Neptune and beyond. Twenty-five years on, it still sends faint signals across the vast cosmic distances from somewhere in the Milky Way.

These sounds have now been mixed with a score written by composer Terry Riley for the Kronos Quartet and an 80-piece choir, co-commissioned by Nasa's surprisingly adventurous art programme (previous beneficiaries have included Andy Warhol and Robert Rauschenberg).

The piece also uses stunning visual information sent back by Voyager (put together by Willie Williams, visual designer for U2 and Bowie) and the result is an overwhelming multimedia epic of a show.

Gurnett explains that space is not, as most people believe, a vacuum but contains a tenuous ionised gas, called a plasma. He designed instruments to record the waves that exist in this plasma in the same way a radio wave is picked up by an antenna. The resultant sounds are organised into different groups by Gurnett.

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Talk to him and he will wax lyrical about what he calls "whistlers" of varying kinds, full of whooshing feedback, crackles, hisses and chirps. One group of sounds he dubs the "dawn chorus", which does indeed sound like an otherworldly aviary.

"I wasn't even aware these sounds existed, which had been sent back across space, and so was utterly intrigued," says Kronos Quartet leader, violinist David Harrington "I see Gurnett as an instrument-maker enabling us to have access to different worlds of sounds. What's amazing about the noises is how organic they are - sometimes you feel they could be the sounds of insects or whales. The visuals, too, make the universe seem conscious - the Sun close up seems like a living body, with a pulsing heart."

Both Harrington and Riley ended up having long, intense discussions with Gurnett about astrophysics. "After eight hours of talking to him I really felt I understood the nature of the universe." Does he still? "No, I've completely forgotten. But for at least a few seconds I felt I had it all figured out."

Terry Riley, a West Coast composer best known for his pioneering minimalist pieces from the 1960s such as Rainbow in Curved Air and In C, has collaborated before with Kronos, most recently in a requiem for Harrington's son Adam.

"I thought of all the composers I knew who would be attracted to a large-scale visionary project like this, and Terry seemed the obvious choice."

On stage, the quartet are surrounded by silver sticks tipped with light and the musicians are armed with fibre-optic wands that trigger the space sounds. Riley's first piece for them had the splendidly hippyish title The Sunrise of the Planetary Dream Collector, so he was always likely to be on the shortlist. Riley also wrote the libretto, changing the piece after September 11 - adding a quote from the writer Alice Walker, "One earth, one people, one love".

"The piece isn't just an abstract imaginative celebration but about humanity," says Harrington. "Those first astronauts all had intense experience seeing the earth as a fragile blue pearl floating in space. It puts our tribal battles in a completely different perspective."

Harrington tells me he spent time both at Nasa and at a jet propulsion centre in Pasadena. "You become aware of the amazing teamwork and creativity needed to send these manmade objects into space."

The recent Columbia shuttle disaster has added poignancy and the awareness of the risky nature of many of these projects, though there are no plans to change the piece to reflect the tragedy.

Riley is just one of hundreds of composers in Harrington's address book - indeed, he must have done more for contemporary composition than any other living individual. While Voyager was on its 25-year tour, Harrington and the Kronos have been on their own tour of contemporary music, with an extraordinary 450 new pieces composed or arranged for the group since the quartet was founded 30 years ago.

Harrington reckons to set aside an hour every day to listen to music he's never heard before. The range and depth of his musical interests is staggering: Kronos have had successful collaborations with everyone from the poet Allen Ginsberg to gipsy group Taraf de Haïdouks and some throat singers from Tuva, in the process selling well over a million records.

The Kronos's eclectic approach can also be experienced the night before Sun Rings in an evening entitled Visual Music, which features music from the likes of John Zorn, Conlon Nancarrow and Icelandic rock band Sigur Ros, all accompanied by videos from assorted filmmakers.

So what is he looking for when he commissions a piece. Originality? "Originality is less important than depth and feeling. I just say to the composer, 'Write us the best thing you've ever written' and quite often they do."

For some artists, 30 years of touring and recording might make them think about slowing down, but not Harrington. Talking about the last Kronos record, Nuevo, which had a Mexican theme, he tells me each day in Mexico City was like a "perfect concert - just the sounds in the streets".

One of the pieces of music that got him interested in string quartets was the Budapest Quartet's version of Beethoven's 12th quartet in E flat Major, which he heard as a 12-year-old. "Just the opening chords I used to play over and over until the vinyl was worn down." Another trigger for the Kronos was hearing George Crumb's Black Angels - "it really expressed the anguish of the Vietnam War". It made him want to start a quartet that was "not afraid to kick ass and be absolutely beautiful and ugly if it has to be. But it had to be expressive of life and tell the story with grace and humour and depth."

When the Kronos Quartet started getting international attention as a new kind of string quartet, with their punky haircuts and string arrangements of such unlikely pieces as Jimi Hendrix's Purple Haze, some dismissed them as a gimmicky fad. But by now it's impossible to doubt their commitment to contemporary music.

Harrington tells me that when the quartet started, he really thought it was possible for music to save the world: "I thought you could do music that was so strong it could stop bullets and tanks." And now? "I still think it's possible to create music that really resonates and that has so much humanity it can create large changes within the listener. We need such music more than ever."

The European premiere of 'Sun Rings' by Terry Riley on March 22 at the Barbican (020 7638 8891). 'Visual Music' is on March 21.